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FrozenGate by Avery

DIY Homemade laser diode driver

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I've found for a red laser powered by around 4-5v, the ideal resistance range is about 5 to 20 ohms, with the larger ohm value producing the minimum mA power and the smaller value setting the maximum mA power. So a good combination would be a 10 ohm multiturn with a 5-10 ohm resistor in series.

Also, mega kudos to rog8811 for all his classy art work ;)
 





rog8811 said:
1k ohm micro size potentiometer 50vdc .01 watts ?
1k ohm 15 turn cermet potentiometer .75 watts?
Click to expand...

Fine adjustment will be far harder with a 1k pot so you need to be extremely careful with the setup!
Drawing below shows the problem

Regards rog8811
Click to expand...

Hey Rog.....

nice pic to explain the different adjustment sensitivities of the LD Driver's pot values...
when using a 1000 Ohm pot instead of the suggested 100 Ohm pot...

This should make it really clear to the new guys......... ;)

Jerry
 
With a red the 15 turn 1k will do the job but you will wind forever until the LD lights then the ma will climb incredibly quickly, as long as you have the correct fixed resistor value it should do no harm though.
I would definately recommend a low ohm pot for a blu-ray though, they are much more fragile than the reds.

As to the input voltage, it has been stated on this thread many times, but not on recent pages.
Red LD needs 3v
Drop out voltage of the regulator 3v
So minimum required voltage is 6v, but as soon as the batteries sag the reg will drop out so go for 7.2v as the ideal.
Blu-ray LD needs 4.5v
Drop out voltage of the regulator 3v
So minimum required voltage is 7.5v, a fully charges pair of 3.6 Li-ion batteries will put out around 8v. I have got away with that in the past, just charge them up frequently

Regards rog8811
 
Has there been any improvement to this basic design? The dropout voltage still seems a little too high for RCR123 use.
 
It has, and always will be 3v drop out but I have used an LM317 /  2 X RCR123A / 803T combinataion without any problems, you just have to charge the batteries more frequently as newly charged ones give a combined voltage of over 8v.

Regards rog8811
 
My LM317T chips aren't gicing a constant 3v dropout, i've found at 4v i get about 2.2v out (min voltage for red and just right for 808 IR according tot he spec sheets for the diodes sold by senkat), at 5v it's 2.8v out and at 6v i get around 3.4v out.

This is measured with a 3 diode load which could produce different resistance compared to a LD and as resistance is linked to current and voltage it might explain my results. Then again, my knowledge of electronics is far from perfect and that explanation could be all wrong  ::)
 
You need to measure the ref voltage to be sure thet the LM317 is still in regulation, you may well find that with 4v in and 2.2v out the regulator is not doing its job properly.

Regards rog8811
 
I have a question. will this work for a PHR803T diode?

I mean, will it drive it enough to burn something effectively, or what kind of power could you get from it?
 
The DDL circuit will work for any laser diode. The amount of power you get depends on the current level you set the driver to. This circuit can provide up to 1.5A of current, which is more than enough for nearly any hobbyist diode. PHRs generally like anywhere between 80-110mA. A 10-ohm resistor works great for blu-rays!
 
Sweet. Thanks. I was looking for a temporary solution until I get a lavadrive.

I can just adjust the pot till I hit 100 or 110 mA, then solder the diode to the leads, right?
 
Yes, in a nutshell.. You must make sure to discharge all capacitors before you connect any laser diode to any driver! Failure to do this will kill your diode.

Also, you'll need a dummy load to use to set the current.. if you don't already have one, more information can be found be searching the forum for 'dummy load'.
 
rog8811 said:
@Daedal, Thankyou for doing that...I have just ordered some regulators.

When it comes to other components I assume that a 200ohm pot would suffice? Will any signal diode do, I have a shed load of 1N4148's.

This next question will really show my ignorance.....But, if this circuit were to be tested on a standard led (rather than the precious laser diode) would the charecteristics, IE current draw, be anywhere near similar?

Regards rog8811

*Hope the mods stick this in the sticky area with sticky stuff...I will be stuck when it falls down the page ;)*

*edit....years after posting this, and having built dozens of these circuits.. easy to follow picture follows ;)
Click to expand...

ok im kind of a newbie here.now what i didnt understand is that we alredy have 2 10 ohm resistors,so why do we need a variable 100 ohm resistor.wont that make it too low
 
risking getting flamed:

the formula for the output current is:

1.25/X=output in Ampere, where X is the value of the resistor(s)

you will need to find out how resistors behave when wired in series and when wired in parallel. in this case the 2x10 ohm resistors could be replaced by 1x5 ohm, i think this is shown this way in the drawing b/c the creator didn't have 1x5 so he took 2x10. actually you don't need the fixed res at all, it's more like a security backup.

otherwise you could set up this driver without the valuable resistor, then you need to calculate the desired output current in advance, since you won't be able to adjust the value.

there is an excel sheet around here making these calculations more comfortable, nevertheless you should try to understand what you are calculating.
 
it's more like a security backup.
Click to expand...

No flaming needed ;) that is the important bit, the fixed resistor ensures that you don't go over the max ma set by the fixed resistor, in this case 5 ohms gives a max of 250ma, the LM317 is capable of giving 1.25 amps with 1ohm resistance.

5ohms was the value for early SenKat reds, I think if you look around you will find that the ones we use now can be run at a higher ma, so lower value fixed resistor.

This thread is excelent but as it has been going for so long it is showing its age ;)

Regards rog8811
 
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